Electrolytic method of coating localized areas of articles



Jan. 16, 1945. A. G RUSSELL 2,367,314

ELECTROLYTIC METHOD OF' 'COATIFR GAL ED AREAS OF ARTICLES Fil'ed June24. 1,941

' (Id/f m vavrofi \E A. 6. RUSSELL rm W produce a sharpline face ofacontinuous Patented'ila n. 16, 19 45 UNITED STATES PATENT OFFICEELECTROLYTIC METHOD OF COATING LOCALIZED AREAS OF ARTICLES Alexander G.Russell, Chicago, Ill., assignor to Western ElectricCompany,'Incorporated, New York, N. Y., a corporation of New YorkApplication June 24,1941, Serial No. 399,463

'6 Claims. (Cl. 204-15) This invention relates to the manufacture ofcoated articles, and more-particularly to methods formaking articleshaving a coating of metal on a selected portion of the article surface.

In certain. types of electrical apparatus, such as communicationequipment, shaped members are often employed to make electrical contactwith other portions of the apparatus and in many instances satisfactoryperformance of the apparatus necessitates that these contact membersreceive and transmit current without appreciable losses or distortion.For example, in certain telephone transmitters. cup-shaped electrodesare used to provide the necessary electrical connectlons with the carbonparticles therein and satisfactory operation of the transmitter dependsin-a large measure upon the contact efliciency 'of these electrodes. Inorder to provide the needed operating and service characteristics, it isoften desirable to use gold or some other noble metal as a contactmaterial on these electrodes and due to the very high cost of thesenoble metals, it is important to restrict their use to the portions ofthe electrode surface whichare actually in con- .tact with the carbon.

In some cases, these electrodes have been 'formed from strip material orturned from rod stock and the formed parts have then been gold plated inspecial racks which we're constructed to concentrate the gold deposit onthe contact areas as much as possible. This former method'has producedsatisfactory electrodes but in the manufacture of certain electrodetypes, which are very small and fragile, particularly careful handlingin the racking operation has been necessary with the result that theracking expense has been undesirably high. Also, it is difllcult ina'rack of this type to provide shielding means that will of demarcationbetween the.

is usually'necessary to make allowances for extending the gold platedand non-plated areas and it deposit beyond the actual contactingsurface'of the electrode in order to insure formation of a satisfactorydeposit over the entire critical area,

with a consequent excess utilization of gold. An object of thisinvention is the provision'of improved methods for producing acontinuous and uniform deposit ofnoble metal on" an accuratelyrestricted portion of an article surface. In accordance with oneembodiment of the invention, the above and other objects'of theinvention are acoompl hed in the manufactureof telephone transmitterelectrodes by roviding one coated strip into an electrode having a'coating of nickel On one surface and exposed brass'or other copperalloy on the other, and finally gold plating the electrodes in a platerwherein the electrodes are immersed loose brass or other copper basealloy strip with acoating or nickel, forming the conventional barrelscription of the accordance "with an edges of the strip hr in anelectrolyte. By use of acombina'tion of electrolyte composition,temperature and current density," a 'uniform' and. continuous film ofgold is produced over the formation of any gold surface. I

A more complete understanding of the invention may be had from thefollowing detailed dedeposit on. the nickel with the appendeddrawing, inwhich Fig.1 is a sectional view of a faced metal strip utilized inproducing transmitter electrodes in accordance with one embodiment ofthe invention;

- Fig. 2 is a sectional-view of an electrode illus-v in which theelectrode is trating the manner formed "from the strip shown in Fig. 1;

Fig. 3-is a plan view of the electrode shown in'Fig. 2;

Fig. 4 is a plan view of an electrode made in the invention to thatillustrated in Figs. 1, 2 and 3; and

Fig. 5 is a sectional view of the electrode shown in Fig. 4, taken onthe lines 5-5 of Fig. 4.

The electrode III cup or dome-shaped body portion, which is ahemisphere, and a narrow and continuous peripheral flange I l extendingfrom the base of the dome-shaped body. When this electrode is assembledin a tra .tter, the outer surface of the dome-shaped body is in contactwith the carbon particles and it is therefore desirable to coat all "ofthis surface uniformly with gold.

In producing an electrode of this type, a strip l3 of brass, bronze, orother copper-base alloy, is

-flrst"sui tably cleaned, for example, in a caustic alloy'used for thispurpose solution. One type of balance copper but contains 35% zinc andthe other alloys containing vided with a thin and uniform facing ofnickel ll, preferably by electroplating in an aqueous solution'of nickelsulphate, sodium chloride and boric acid. v

In this plating operation only one face and the "coating. In'nickel-plating thin strip material, it

is convenient to wrap the 1 platingflrack having a" surface of 'softrubber strip and to support the rack and strip in the nickel-p'lating-bath. In this manner, access the platlng' solution to theunder-surface of the s-trip in contact "with the rack, and theformastrip spirally around a whih-closeiy enga es t e under-surface ofthe tion cr mmin thereon, is prevented. In another method, suitable forcoating either thin or thick strip material, 7

through the "plating bath in contact with a parthe strip is conductedtially-immersed cylindrical roller faced with soft rubber. This rollershould be sufliciently large the exposed brass area'without inventiontaken in conjunction alternative embodiment of shown in Figs. 2 and 3has a predominantly copper are i also suitable. The cleaned alloy stripis next proare provided with the nickel in diameter so that one .face ofthe strip can be held in close contact with the roller facing byvtension applied to the strip during complete passage of the stripthrough the plating bath, thereby excluding plating solution and metaldeposit .irom the engaged face of the strip. Only a very form inthickness. Therefore, the plating action is continued only long enoughtoproduce a continuous nickel film on the strip face.

In the next operation, the nickelfaced strip is formed by conventionalmeans into the electrode,

shape, as shown in Figs. 2. and 3, with the nickel coating on the insidesurface of the dome or cup and the brass surface on the outside of thedome.

The formed electrode is next gold plated and this operation can beperformed without the use of racks or other special supports in a barrelplater of'the conventional type. The usual barrel plater comprises achamber which contains an electrolyte, a movable mesh basket in thechamher for supporting the articles to be plated in the electrolyte, andplating electrodes which are suitably connected in a power circuit. Inone type .ing the plating operation in accordance with the total numberof articles or electrodes connected in the plating circuit at any onetime.

of barrel plater that is satisfactory for this purpose, the mesh basket,made of insulating ma-' terial, is cylindrical in form and is supportedon a rotatable shaft. The anodes are positioned in the electrolyteoutside of the bsket and a plurality of cathode contacts are mountedinside the basket basket, current is transmitted from article toarticleby contact and the current density varies in the course of theplating operation in accordancewith the number of articles that arereceiving current, either directly from the cathode Y contacts orthrough article to article contact, at

any one time. It has been discovered that despite this inevitablevariation in current density, a satisfactory gold'coating l5 can beapplied on the brass area and the deposit of gold on the nickel avoided.This is accomplished with a combination of electrolyte compositions,electrolyte temperature and current density values.

The following electrolyte composition is preferred:

Ounces per gallon of water Sodium gold cyanide 1.5

Potassium cyanide r 6.0

Potassium hydroxide c .50

When this particular composition is employed,

the electrolyte is maintained at a temperature of the platingoperaapproximately 120 F. during tion.

Some deviation from the above listed specific constituent proportions ispermissible and the following ranges can be used, particularly ifaccompanying adjustments are made in other process' factors:

Ounces per gallon of water 'sodiumgold cyanide e .75 to 2.5 Potassiumcyanide 3.0 to 8.0 Potassi um hydroxide .20 to .70

In using these solutions, the solution temperature is maintained between105F. and 135 F.

are obtained if the and, in general, best results higher temperaturesare employed with the more concentrated solutions.

Sodium and potassium compounds are employed preferably in-thecombinations shown in the above table in making up these solutions but,in some instances, a sodium compound can be substituted for a potassiumcompound or a potassium compound for a sodium compound in chemicallyequivalent proportions.

As stated above, the current density varies dur- The number ofelectrodes placed in the basket, the quantity of solution in thecontainer, the spacing of the cathode contacts, and the rotational speedof the basket are coordinated to minimize this current density variationbut it cannot be completely eliminated. However, it is possible tosegregate the gold deposit to the brass or copper alloy area bymaintaining the average current density, based on the combined areas ofall the .electrodes in the basket, within certain limits.

This average current density should be maintained between .2 and .6ampere per square foot of article surface and preferably established at.4 ampere per square foot of electrode surface. This average value isbased on the total .area of all the electrodes in process. The currentdensity will exceed the average values at some stage of the process butunder the' described conditions the maximum values do not reach aharmful intensity or duration.

The completed electrodes have a continuous film of gold 15 over theentire exposed brass area and the gold film terminates abruptly at thelines of demarcation between the nickel-coated and the exposed brass orcopper alloy areas.

Another type of transmitter electrode which is produced by analternative method within the scope of the invention is shown in Figs. 4and 5. This electrode 20, which is of substantially heavier constructionthan the electrode shown in Fig. 3, has a dome-shaped or cup-shaped body22 with a circular opening 23 in its central portion and an extensiveperipheral flange 24 around the domeshaped body. When an electrode ofthis type is mounted in a telephone transmitter, the flange serves as amountingand the inner, or concave, surface of the dome is in contactwith the carbon particles.

In producing this type of electrode, a shape is initially produced frombrass or other copper alloy sheet by means of conventional forming diesor'turned from rod stock on a screw machine or the like. The same copperbase alloy compositions used for the small electrodes ID are suitablefor this heavier electrode 20 also.

In the forming or turning operation all portionsof the electrode, withthe exception of the concave or inner surface of the dome, are formedaccurately to the final dimensions, with allow-v ances for coatings tobe applied subsequently. The concave portion of the dome is formedoversize, or with'a shorter radius than that finally required, so thatexcess base or alloy material is provided at this portion of the body.

The shaped articles are then nickel-plated by a conventional process, toprovide a thin and continuous coating or layer of nickel 25 over theentire article surface.

' Next, a machining operation is applied to the inner or concave face ofthedome to increase the radius ofthis configuration. In this operation,

which can be performed on a lathe or screw ma- 'quired and square footof article cup and exposed alloy on cup, immersing a quantity of theformed articles I age current "except the inside surface of the dome,where the brass or other base material is exposed.

The machined electrode is then gold plated in a barrel plater to apply agold coating 26 on the inner surface of the dome. In this operation, thesame combination of electrolyte composition, solution temperature andaverage current density used for plating the small electrode, as abovedescribed, are employed.

The completed electrodes, a continuous coating of gold which electricalproperties and is accurately restricted to those portions of theelectrode surfaces which are actually in contact with the carbonparticles when'the electrodes are assembled-in a transmitter. The goldcoating is very uniform in thick ness, which obviates the-necessity forheavy platin to assure complete minimum coverage and results in furthereconomies in the use of gold. In the processing operations, racking isnot rethe electrodes can be processed in quantities with minimumhandling and without special equipment.

It will be apparent that modifications of the invention embodimentspecifically described herein can be made to adapt the invention tovarious art cles and conditions and it is to be understood that theinvention is limited only by the scope of the appended claims, a

What is claimed is: v

1. In a method for making an article having different portions of itssurface coated with-different metals, the steps of forming the articlefrom a copper base alloy, producing a n ckel coating on only a portionof the article surface. immersing a quantity of the formed articlesloosely in an aqueous electrolyte comprising from ."15 to 2.5 ounces ofsodium gold.cyanide, 3 to 8 ounces of potassium cyanide and .20 to .70ounce of potassium hydroxide per gallon of water, and plating thearticles in said electrolyte at an average current density ranging from.2 to .6 ampere per surface while maintaining the electrolyte at atemperature between 105? F. and 135 F. to cause the deposit of a goldfilm on the alloy surfacewithout causing the deposit of er both types,have gold on the nickel surface;

2. In a method for making a cup-shaped article having different portionsof its surface coated the steps of electrodeposit face of a copper alloywith diiferent metals, ing a layer of nickel on one strip, forming thestrip into a cup-shaped article having the nickel coating on one surfaceof the loosely in an aqueous electrolyte comprising from .75' to 2.5.ounces of sodium gold cyanide. 3 to i! ounces of potassium cyanide'and.20 to .70 ounce of potassium hydroxide per gallon of water, and

.. plating the articles in said electrolyte at an aver-- density rangingfrom .2 to.. 6 ampere,

per square foot of article surface while mainhas excellentv the othersurface of the cup surface from Gil taining the temperature of theelectrolyte-between 1 F. and 135 F. to cause the deposit of a continuous' gold film on the alloy surface without causing the deposit ofany gold on the nickel surface;

-3. In a method of different portions of its surface making an articlehaving coated with dif-.

density ranging from loosely in an aqueous immersing aquantity of theformed articles loosely in an aqueous electrolyte comprising about 1.5ounces of sodium gold cyanide, 6 ounces of potassium cyanide and .50ounce of potassium hydroxide per gallon of water, and plating thearticles in said electrolyte at an average current density around .4ampere per square foot of article surface while. maintaining theelectrolyte at a temperature of about F. to cause the deposit of auniform gold film on the alloy surface with out causing the deposit ofany gold on the nickel surface.

4. In a method of making a cup-shaped transmitter electrode, the stepsof forming a cupshaped electrode from a copper base alloy,electrodepositing a layer of nickel on the entire surface of theelectrode, removing the nickel layer from only one surface of thecupportion of the electrode, immersing a quantity of the electrodeselectrolyte comprising from .75 t 2.5 ounces of sodium gold cyanide, 3to 8 ounces of potassium cyanide and .20 to .70 ounce of potassiumhydroxide per gallon of water, and plating the electrodes in saidelectrolyte at an average current density ranging from .2 to .6 ampereper square foot of article surface while maintaining the temperature ofthe electrolyte between 105 F. and F. to cause the deposit of acontinuous gold film on the surface of the which the nickel layer wasremoved without causing the' deposit of any gold on the nickel remainingon the remaining portions of the electrode. a

5. In a method for making a cup-shaped transmitter electrode, the stepsof forming a copper base alloy into a body having the general sliapedesired in the completed electrode and excess material on the concavesurface of the cup portion, electrodepositing a layer of 'nickel on theentire surface of said body, machining the nickel coated body. to removethe nickel layer and the excess alloy from the concave surface of thecup portion, immersing a quantity of the machined bodies loosely in anaqueous electrolyte comprising from .75 to 2.5 ounces of sodium goldcyanide, 3 to 8 ounces of potassium cyanide and .20 to .10 ounce ofpotassium hydroxide per gallon of water, and plating the bodies in saidelectrolyte at an average current density ranging from .2 to .6 ampereper square foot of body surface while maintaining the. temperature ofthe electrolyte between 105 F. and 135F. to cause the deposit of acontinuous gold'nlm on the concave surface of the cup withoutcaus'ingthe deposit of any gold on any other portion of the body.

6. A method of making an article having different portions of itssurface coated with different metals comprising providing a nickelcoating on a selected portion of a copper basealloy article,

an aqueous solution of .75 to 2.5 ounces of sodium gold cyanide; anide,and .20 to .70 ounce of potassium hydroxide per gallon of water,maintaining the at a temperature ofsubstantially 105 F.-to 135 F., andpassing an electric current at a current .2 to .6 ampere per square footof surface through coating to the article only in the portion in whichit i free of nickel.

3.0 to 8.0 ounces of potassium cyelectrolyte the article to apply a goldI ALEXAND G. RUSSELL,

